Design And Fabrication Of Terahertz Microbolometers And Filters Based On Metamaterials

The wavelength of the terahertz?THz?wave is between the infrared and the microwave bands,which has some unique characteristics such as high broadband,high transparency,transient and so on.With the development of THz technology,THz detection has attracted much attention in the fields of imaging,explosives detection,identification,communication and other fields.However,due to the low photon energy of the THz wave,the THz detector still faces the problems of low absorption and high ambient noise.Because of the weak response in the THz band,the conventional devices and materials are difficult to meet the requirements of the THz detectors.Aiming at the two key problems of THz absorption and filtering in uncooled terahertz detector,this thesis focused on the structure design and simulation,manufacture and performance test of the metamaterials-based microbolometer and filter.The main contents of this thesis are as follows:By analyzing the response characteristics of electrical split-ring resonators?eSRRs?metamaterial absorber under terahertz wave in different structure parameters,the control laws of dielectric layer on metamaterial absorber were studied.It was found that there are two kinds of low-order resonant absorption modes:the LC resonance absorption and the 1st order dipole resonance absorption.It was worth noting that the two modes of resonance absorption exhibited opposite trend if changing the thickness of dielectric layer.In thick absorber,LC resonance absorption dominates.When the thickness of the dielectric layer was increased,the resonance absorption of LC became stronger while the resonance absorption of the 1st order dipole weakened.On the contrary,the 1st order dipole resonance absorption dominates in the thin absorber.When the thickness of the dielectric layer was decreased,the resonance absorption of the 1st order dipole became stronger,while the LC resonance absorption weakened.Meanwhile,the response frequency of eSRRs absorber would change significantly if the dielectric constant of dielectric layer was changed.The larger the dielectric constant of the dielectric layer was,the lower the response frequency achieved.Based on this rule,the frequency equation was proposed.When the other parameters were constant,the frequency of the absorber could be quickly calculated according to the frequency equation when the new material was used to replace the original dielectric material.Based on the high absorption characteristics of rectangular metamaterial absorber,a terahertz microbolometer was designed and fabricated.Different from conventional microbolometer,rectangular metamaterial absorber serve as terahertz absorption unit on the microbridge.In the finite element analysis model,the optical,thermal and mechanical properties of THz microbolometer under different metamaterial thickness,bridge leg width and bridge thickness were simulated and studied.When the thickness of the dielectric layer,the leg width,the thickness of microbridge were 0.9?m,1.2?m,0.3?m,respectively,some values of the THz microbolometer were simulated at 3.9 THz.These simulation values were 41.2%for absorption rate,0.231k for temperature rise,0.426?m for the deformation of microbridge.With the optimized structure,a terahertz microbolometer based on rectangular metamaterial absorber was fabricated by micro-electromechanical systems?MEMS?process.The sizes of the microbridge structure were 37×37?m² unit and 120×120 array.The results of Fourier transform infrared spectroscopy?FTIR?test showed that the terahertz microbolometer had a absorption peak of 31.5%at 3.93 THz,which exhibited good absorption response in terahertz wave.Using the film deposition and photolithography technology,a substrate-free hollow fishnet metamaterial?HFMM?filter was fabricated by silicon etching.From the results of FTIR and terahertz time domain spectroscopy?THz-TDS?,one could see that the transmission of the single-layer HFMM at 3.75 THz was 88.1%,and the full width at half maximum was 2.79 THz.This means that the metamaterials-based filter had good filtering characteristics.By analyzing the permittivity and permeability,the behaviors of electric resonance and magnetic resonance of the HFMM were studied.Meanwhile,the effects of size parameters on the characteristics were discussed numerically.It was worth noting that the multi-layered filters were able to fabricated easily by stacking the single-layer filter.Compared with single-layer HFMM,the transmission peak of multilayer filter was more steep and exhibited better out-of-band rejection.Based on the high reflection properties of TiO₂ all-dielectric metamaterials,a new type of Fabry-Perot?F-P?filter was designed and studied.Because of no metal structure,such type of filter effectively reduced ohmic loss.By analyzing the permittivity and permeability,the influences of size parameters on the reflection properties of all-dielectric metamaterials were systematically studied.The simulated results showed that the reflection of all-dielectric metamaterials was higher than 95.4%in the band of 2.49³.08 THz.Compared with the conventional F-P filters based on distributed Bragg mirrors,the thickness of the cavity was reduced from?/2 to?/18 in the new F-P filter based on all-dielectric metamaterials.It was worth noting that the new F-P filter not only had the characteristics of small cavity and low ohmic loss,but also could adjust the response frequency by changing the thickness of the cavity.